The networking of control units, sensors and actuators with the aid of a communication system, that is, a bus system, has increased in recent years in the construction of modern motor vehicles and in machine construction, for example in the field of machine tools and in automation. In this context, synergy effects due to the distribution of functions to several control units or other users may be achieved. These are referred to as distributed systems. The communication between different users of such distributed systems may occur more and more via a bus or a bus system. The communication traffic on the bus system, access and reception mechanisms, as well as error recoveries may be governed via a protocol.
A bus system of this type having a corresponding protocol is the LIN bus (Local Interconnect Network). The LIN bus is a master-slave bus whose users are connected via a logic bus line. A maximum of one master and up to 64 slaves belong to each bus. An unshielded physical single-wire line is used as the transmission medium. The LIN protocol divides the transmitting and receiving process into two tasks. The master task deals with synchronization and addressing, and the slave task deals with the data. A master is able to execute both the master task and the slave task, while a slave is able to execute only the slave task. A slave-to-slave data exchange may be performed via special addressing. In this context, each data transfer is made up of a messaging or communications frame in which both the synchronization and the data information are transmitted. The individual sections of the message, the so-called byte fields, have the same format of a serial interface in the case of 8N1 transmission, i.e. 8 data bits and 1 stop bit. At the beginning of each message frame, the master sends synchronization information, the so-called SynchBreak, in order to recover slaves from a possible idle state and enable synchronization. The SynchField follows the SynchBreak. In this case, the master sends a hexadecimal pattern to enable the slave to be synchronized, for example with the aid of trailing edges, recessive toward dominant. The next information identifier or identifier field (IdentField) provides information about the content and the length of the subsequent data fields and hence of the message frame.
Single-wire bus systems of this type, like the LIN bus, may be used with greater frequency today for cost reasons in sub-bus systems, for example, in motor vehicles. In this case, the bus access for the LIN bus is based on a strict master/slave method, as mentioned. The LIN slaves in this method may not signal a local event to the master. Consequently, depending on the application and data volume, this may result in a high bus load, even with few time-critical signals, due to the time-intensive polling of the slaves, i.e., the time-intensive ascertainment of readiness for receiving or sending.
Thus, it may be shown that the related art, in particular the LIN bus, may not be capable in every respect of supplying optimal results. Therefore, the existing LIN bus may require expansion so that the subordinate users in the bus system, i.e. the slaves, are able to send out information by themselves.